x86 single_step: TIF_FORCED_TF

This changes the single-step support to use a new thread_info flag
TIF_FORCED_TF instead of the PT_DTRACE flag in task_struct.ptrace.
This keeps arch implementation uses out of this non-arch field.

This changes the ptrace access to eflags to mask TF and maintain
the TIF_FORCED_TF flag directly if userland sets TF, instead of
relying on ptrace_signal_deliver.  The 64-bit and 32-bit kernels
are harmonized on this same behavior.  The ptrace_signal_deliver
approach works now, but this change makes the low-level register
access code reliable when called from different contexts than a
ptrace stop, which will be possible in the future.

The 64-bit do_debug exception handler is also changed not to clear TF
from user-mode registers.  This matches the 32-bit kernel's behavior.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 2 insertions, 9 deletions

diff --git a/include/asm-x86/signal.h b/include/asm-x86/signal.h
index 987a422a2c78..aee7eca585ab 100644
--- a/include/asm-x86/signal.h
+++ b/include/asm-x86/signal.h
@@ -245,21 +245,14 @@ static __inline__ int sigfindinword(unsigned long word)
 
 struct pt_regs;
 
-#define ptrace_signal_deliver(regs, cookie)             \
-        do {                                            \
-                if (current->ptrace & PT_DTRACE) {      \
-                        current->ptrace &= ~PT_DTRACE;  \
-                        (regs)->eflags &= ~TF_MASK;     \
-                }                                       \
-        } while (0)
-
 #else /* __i386__ */
 
 #undef __HAVE_ARCH_SIG_BITOPS
 
+#endif /* !__i386__ */
+
 #define ptrace_signal_deliver(regs, cookie) do { } while (0)
 
-#endif /* !__i386__ */
 #endif /* __KERNEL__ */
 #endif /* __ASSEMBLY__ */